Evoforce wrote:But...If the outside ram air is more powerful than the high fan setting, opening that plate might introduce more powerful ram air and drown out any cooled air inside as well as where that top of battery HV connector is located at half pack. Uneven cooling of the pack just doesn't make sense either. In my climate, engineered cabin air cars are also needing to have their batteries replaced. Most people only drive their cars around 4% of the time. So during the off time here, it still stews in the heat, especially after driving and charging. That doesn't even address people here that then park in their hot garage.

This thread is intended to help people experiencing elevated battery temperatures due to repeated fast charging on long trips. These are not temperatures you would ever expect to see parked in a parking garage or even parked on the street. I’m only suggesting the use of the air-conditioning while fast charging, not while driving.

There is nothing unusual about running the air-conditioning while fast charging. The Nissan Leaf battery pack is designed to withstand subzero and extremely high ambient temperatures. I can’t imagine that a little air-conditioning is going to hurt the pack.

I have been promoting fast charging until it tapers down to L2 speeds. If we are trying to use the air-conditioning, we may want to wait for the fast charger to taper down to 0 and then kick off. The charger would be powering the air-conditioning and extra time cooling the battery pack could be more than recovered in faster charging speeds at the next fast charge.

We might also want to wait a few minutes after charger stop before before we head off. This would allow more of the battery pack heat to get absorbed by the cool cabin before we disrupt the heat flow by driving.

But...If the outside ram air is more powerful than the high fan setting, opening that plate might introduce more powerful ram air and drown out any cooled air inside as well as where that top of battery HV connector is located at half pack.

I have never driven a car in which "outside ram air" is more powerful than the ventilation blower. Having the windows open produces more airflow of course, but that air isn't cooled. I also think you are confused about what I proposed, which is CLOSING the rear vent in order to direct the cooled cabin air down the battery cooling tunnel. Unless you are actually referring to the cooling tunnel when talking about "outside ram air" in which case the effect could be anything from increased cooling, through no net effect, to actual warming, depending on the ambient air temp.

In short, it isn't clear to me exactly what you are talking about...

What I must have thought is that the discussion was including trying to cool the pack also while the car was being driven and the plate at the HV connection remaining off while in transit. I just find it sad that such lengths are still having to be tried in order to fix a factory design problem.

TexasLeaf wrote:I have been promoting fast charging until it tapers down to L2 speeds. If we are trying to use the air-conditioning, we may want to wait for the fast charger to taper down to 0 and then kick off. The charger would be powering the air-conditioning and extra time cooling the battery pack could be more than recovered in faster charging speeds at the next fast charge.

We might also want to wait a few minutes after charger stop before before we head off. This would allow more of the battery pack heat to get absorbed by the cool cabin before we disrupt the heat flow by driving.

Thank you for giving me a clear understanding of what you are driving at. I now understand that you are addressing how to get the most out of your car on longer trips.

I do want to say though, ambient temperature very much does negatively effect the Nissan Leaf battery in hot climates. Even cooling or heating of the pack is very important. Just keep that in mind. Individual battery cells need to degrade at the same rate. Your pack is only as good as your weakest cell.

Good luck on your experiments, we could use a breakthrough on these cars that they chose not to give a liquid TMS. Hopefully 2019 will be the year that Nissan turns their bad battery legacy around!

Edited: To be more clear on description wording, individual batteries was changed to cells.

Last edited by Evoforce on Fri Aug 03, 2018 12:49 pm, edited 1 time in total.

I wanted to find out exactly how the fresh air got out of the cabin of my 2018 Leaf so I did a tissue test. I found that the fresh air leaves the cabin through two large grilles near the lights on both sides in the trunk. The air flow was so strong that the tissue actually stuck to the grilles.

I knew that the air going through those grilles had little chance of cooling the battery. So I decided to remove the Service Plug plate and see if I could get fresh air through the port. The Service Plug plate was real easy to remove, all you need is a flat blade screwdriver and a 10 mm socket wrench.

With the plate removed and the AC in Fresh Air mode there was a torrent of air going through the Service Plug port. There was so much air going through the port that I couldn't get the tissue to stay against the grilles in the trunk anymore. With the power for the AC compressor coming off the battery, I turned the AC temperature down as low as it would go and I turned the fan up as high as it would go.

The battery temperature had already equalized with the ambient temperature. After about half an hour the battery temperature had dropped a full degree F according to LeafSpy. All three temperature sensors showed an uniform temperature drop.

Using the Service Plug port for additional battery cooling was very easy to do. It worked so well that it makes me think that the Service Plug port is actually intended to be used for supplemental battery cooling. At the moment I can't think of any reason not to use the Service Plug port for supplemental battery cooling.

It would make sense to remove the Service Plug plate and cool the battery with cabin air on long trips where multiple fast charging stops were planned. For normal day to day driving, the plate should be left on to keep insects and varmints out of the car. My test was performed on a 100+ degree F day with the battery temperature equalized with the environment but I would expect even greater benefit when battery was hot and the outdoor air temperature was cold.

This isn't surprising, except for how much air flows through the inside port. Good job on the testing. Depending on driving conditions it should also be possible, at times, to use the A/C to cool the pack while driving. The biggest mod to do that would be to try to redirect air from the A/C condenser around the pack, rather than have it heat the air in the cooling tunnel. Otherwise you'd mainly want to try using it in crosswinds and tailwinds.

I performed a few more test using air conditioning to cool the battery. I am now confident that removing the Service Plug plate and pushing cold air through the port gives significant benefit in cooling the battery. It's not a silver bullet but I think using the air conditioner to help cool the battery will mitigate the worst problems associated with battery overheating.

I wanted to see if there were any routes for fresh air to leave the cabin other than the grilles in the trunk. I taped up the grilles in the trunk, left the Service Plug port closed, turned the AC to Fresh Air and turned the fan on full. If the grilles were the only way for air to exit the cabin then the fresh air coming out of the vents should have almost stopped with the grilles taped up but I could hard tell a difference in air flow.

There was still a lot of fresh air coming out of the vents with the vents taped up and I could not figure out where the air was going. It's possible the fresh air is getting pushed to the battery compartment somewhere but I can't figure out where. For now I'm just going to assume that the fresh is making it's way to the relief vents behind the bumper but I'm still going to tape up the grilles in the trunk and take off the Service Plug plate so I can do AC battery cooling when I go on long trips.

There are two incidents worth reporting that occurred this last weekend. Once I was able to stop the battery temperature rising beyond 124 degrees F by turning on Fresh Air mode while driving at 60 mph and again I was able to stop temperature rising beyond 108 degrees F while charging at 18 kW. Both of these incidents occurred when it was about 100 degrees F outside and I had been on the road a while.

There are a couple of techniques I have adopted for air condition cooling of the battery. I have started to put up a sunscreen in the front window to reduce the load on the AC compressor. I have also started putting the AC in Recirculation mode until the cabin cools down and then I put the AC in Fresh Air mode to push the colder cabin air through the Service Plug port.

I bought a thermostat for the cabin so I can accurately monitor cabin temperature. The AC can only cool the cabin temperature to about 20 degrees F below ambient so when it's 100+ degrees F outside the benefits of AC battery cooling is limited. I'm looking forward to cooler weather so I can test the benefits of AC battery cooling and cooler weather combined.

With the techniques I have adopted I can go three or four fast charges before my Leaf shows 11 bar temperatures in this Texas heat. It takes all day to test these battery temperature control techniques over multiple fast charges. I have not yet performed a serious long distance test using these new AC battery cooling techniques I have adopted and I don't know when I will find time to do so.

For a car that's not supposed to be able to travel long distances, I sure am putting a lot of miles on my 2018 Leaf with all these battery temperature tests. I've put almost 5,000 miles on my Leaf since I leased it in March. I've pretty much lost all apprehension about driving this car very long distances as long as I can find fast charging stations along my route.

I will provide a post if I have any new AC battery cooling results to report.

You'll also want to post regular LeafSpy results. Please also post them in the 40kwh battery topic. One word of caution: it's looking to me like pack temperatures above as low as 60F may produce more degradation. (I won't have a better idea of that until later in the Fall.) If this is the case then cooling the pack to seven bars isn't going to solve that particular problem, just reduce it somewhat.

LeftieBiker wrote:You'll also want to post regular LeafSpy results. Please also post them in the 40kwh battery topic. One word of caution: it's looking to me like pack temperatures above as low as 60F may produce more degradation. (I won't have a better idea of that until later in the Fall.) If this is the case then cooling the pack to seven bars isn't going to solve that particular problem, just reduce it somewhat.

Batteries degrade. They degrade slower at 60F than at 70F. Even slower at 50F. Probably slowest somewhere near 0C/32F. This is a complex chemical reaction. See:

There are different reactions that happen below about 0C, and batteries probably degrade faster below about 0C. Battery heater tries to keep battery above -20C, unless you have one of the early LEAFs without a battery heater.

I'm not sure I would modify the car to add battery cooling. The possibility of getting condensation where there shouldn't be any raises the worry of battery fires at worst case. Sure, unlikely, but Li-ion batteries don't mix with moisture very well. See the 2012 Zero example: